printing quality b&w photo book

[jos__garese]

I'd like to know what "300 line screen" means, a sort of standard for quality

photo-book printing. (One can frequently read about a black & white photo book:

"duotones, 300-line screen"). The cutting edge seems to be "600 line screen". Do

these measurements relate in any way to dpi's (dots per inch), or are they

another thing altogether and if so, what exactly? Thanks in advance for your

replies.

[mikep]

In traditional printing photos need to be screened for the press, 300 lines is a high amount per inch. Newspaper is about 60 lpi.

[ilkka]

If you put a good loupe on an offset printed page, you can count how many dots per inch there is (actually, you need to count dots per mm and multiply by 25). Good quality 'coffee table' books would have about 175-200 dpi. In the printing industry, this seems to be referred to as 350 or 400 line screen. I have never heard of 600 line screen. If it is duotone, there would be another set of grey dots, aligned some 15, 30 or 60 degrees from the black ones. Somewhere I read a rule of thumb that suggested to supply images with ppi 1.5 times the line screen, for best quality.

[dave_redmann]

It sounds to me like some people may be confusing lines per inch (lpi), pixels per inch (ppi), and dots per inch (dpi). The difference is huge!

 

Lines and dots describe the basic 'building blocks' of an image made with only one (B&W) or four (color) colors of ink. Pixels describe continuous tone (or simulated continuous tone) building blocks of an image.

 

In, say, a traditionally-printed newspaper image, on any given spot in an image, you either had black ink or you didn't--period. To make something look like gray, the image is divided into areas, and the printer puts either a bigger or a smaller black dot to fool your eyes, when you look from a distance, into seeing either darker or lighter gray, respectively. Typically, the positioning of these dots was along a series of parallel lines; a 100 lpi screen means that the lines are 1/100th of an inch apart, as I understand it. Typically the lines are neither horizontal nor vertical, but at an angle, which makes them less visible. The more lines you use, the closer together they become, the less visible the individual dots become, and the more closely the image looks like it has real shades of gray, instead of black dots.

 

Traditional color printing is similar, except that in addition to black ink (referred to as K), you also have cyan (sky blue), magenta (pinkish-purple), and yellow ink--CMYK.

 

Inkjet printers have to do the same thing. They only have 3, 4, 6, 8, however many colors of ink (none has more than 11 or 12, I think). In order to make the appearance of more colors--I seem to recall reading that our eyes can differentiate about a billion different colors--you have to use differing combinations of the 6 or whatever you've got. An inkjet printer might say it prints 2400 dpi, but it cannot print full color at more than, say, 300 ppi. The more dots you use for each pixel, the better you can approximate all the different colors. Each continuous-tone pixel will contain varying numbers of ink-colored dots. By controling the proportion of dots from each ink color in each pixel, the printer can do a pretty good job of fooling your eye.

 

So although I cannot give you advice on the latest standards in the printing industry, I have two main thoughts: (1) anybody who wants to equate a 300-line screen for an ink-printed image with a 300 ppi image from a Fuji Frontier is, to a certain extent, mixing apples and oranges and is not to be relied on, and (2) getting real photo quality in a printed book seems tough--shadow detail seems hard to maintain, and highlight detail can be.

 

Good luck.

[dave_redmann]

P.S.

 

I should qualitfy my statement that inkjet printers to the same thing--by same, I mean that they also mix varying proportions of the colors of their ink to produce other colors. I did not mean to suggest that any given inkjet printer uses lines / screens like newspaper presses use, although at least at times there has been software for some inkjets to print images this way (I even played around with it back in the day with my original Apple StyleWriter 360 dpi B&W inkjet--interesting and educational, but only marginally useful).

 

Also, you will note that CMYK are opposites / negatives of RBG and white.

[jos__garese]

Thanks Dave. Your reply is clear and instructive. I have now a better idea of lpi's.